Windows shape how a home feels more than most people expect. They bring in light and views, but they also let heat in and out. A room with the wrong glass can bake in summer and feel chilly all winter. Getting the choice right makes a real difference in a renovation or new build.
This post explains the main window glazing options for Australian homes. It draws on guidance from Your Home, the Australian Government guide to sustainable homes. We cover glass types, frames, ratings and simple upgrades for windows you already have. The right answer depends a lot on your climate and the way each window faces.
Why windows matter so much for comfort
Glass is a poor insulator compared with an insulated wall. Your Home says up to 40% of a home’s heating energy can be lost through windows. It also says up to 87% of a home’s heat can be gained through them. Those figures explain why a sunny room can be so hard to keep cool.
Windows also affect how much daylight you get and how a room looks. Good glazing can keep the light while cutting the heat. That balance is what the ratings below try to measure. It helps to understand them before you visit a window supplier.
The two numbers to look for
The first number is the U value. It measures how easily heat passes through the whole window, including the frame, glass and seals. A lower U value means better insulation in both winter and summer. It matters most in cooler climates.
The second number is the solar heat gain coefficient, or SHGC. It shows how much of the sun’s heat a window lets through, on a scale from 0 to 1. A lower SHGC means less solar heat comes in. Your Home notes that hot climates favour a low SHGC.
These numbers appear on ratings from the Window Energy Rating Scheme, known as WERS. WERS rates windows, skylights and glazed doors. It lists the U value, SHGC, air leakage and visible light, plus star ratings for heating and cooling. Your Home suggests checking that ratings follow the Australian Fenestration Rating Council requirements.
Single glazing and double glazing
Double glazing uses two panes of glass sealed with a gap between them. These are called insulated glass units. Your Home says they give the best results in all climates, not just cold ones. A gap of 12 millimetres is the preferred size, and the cavity can be filled with argon gas.
The difference shows up clearly in Your Home’s example figures. A single glazed aluminium window with clear glass has a U value of about 6.9. A double glazed timber or uPVC window comes in at about 3.0. Those are indicative figures only, but they show how much the glass and frame together can change.
The seal on a double glazed unit matters. Your Home says the cavity must be well sealed and contain a drying agent. Otherwise moisture can condense between the panes. Buy from a supplier who can explain how their units are made and sealed.
Coatings and tints on the glass
Low emissivity glass, often called low E glass, has a thin coating that controls heat. Your Home says these coatings can greatly improve both the U value and the SHGC. Some versions let daylight in while stopping heat escaping in winter. Others cut summer heat gain while keeping good light levels.
The type of coating affects how it can be used. Soft coatings must sit inside the sealed gap of a double glazed unit. Hard coatings are baked on during manufacture and are tougher. Your Home also warns that coatings must be installed correctly or they can underperform.
Sun through the glass also fades fabrics and timber over time. Window coverings help with that as well as heat. Our post on indoor shutters that protect furniture from fading covers that side of the problem. Better glass and good coverings work well together.
Choosing a frame material
The frame also has a big effect on performance. Aluminium is light, strong and durable, but it conducts heat well. A thermal break is a strip of low conductivity material between the inner and outer parts of the frame. It reduces the heat that travels through aluminium.
Timber is a good natural insulator but needs good draught seals. Your Home suggests choosing timber from a sustainably managed forest. uPVC insulates about as well as timber and seals well, though colour choices are more limited. Composite frames pair an aluminium outside with a timber or uPVC inside.
Timber frames need regular care to stay sound. Painting them on the right kind of day helps the finish last. Our guide to scheduling exterior house painting covers the weather to aim for. Plan frame painting into the same job if you can.
Matching glass to the way each window faces
One glass type for the whole house is simple, but rarely the best choice. Your Home says windows facing north in temperate climates can have a higher SHGC with fixed shading. That shading should block summer sun but let winter sun in. Cities like Sydney, Melbourne and Adelaide fall into this group.
East and west windows are harder to manage. Your Home suggests a low SHGC for these, especially on large windows. Adjustable shading on the outside is preferred. South facing windows can take any SHGC because they get little direct sun.
Your Home notes that matching glass to orientation may gain at least half a star in energy rating. It is worth asking your supplier to quote this way. A low U value helps in every direction.
Floors near big windows can soak up the sun too. If you are replacing floors at the same time, think about how the light falls on them. Our post on indoor epoxy flooring for WA homes looks at one hard floor option. Plan glass and flooring choices together in rooms that face the sun.
Upgrades for windows you already have
Replacing every window is a big cost. Secondary glazing is a cheaper option for some homes. It adds a sheet of acrylic or glass to the inside of the existing frame. Your Home says it improves insulation, air leakage and noise, though not as much as a factory made unit.
Some window films can halve a window’s SHGC, according to Your Home. That helps on east and west windows or in hot climates. Films also reduce the light coming in. Your Home recommends an accredited installer to avoid the glass cracking from heat.
Curtains and blinds are the simplest step. Your Home says snug curtains with pelmets and no gaps trap still air near the glass. Heavy or layered fabrics insulate better. Small savings around the house add up, much like the ideas in our post on simple plumbing tips to save on water bills.
The full Your Home guide to glazing has more detail and worked examples. It is a useful read before you talk to a supplier. Take your window sizes and the direction each one faces with you. That makes quotes easier to compare.
Frequently asked questions
Is double glazing worth it in a warm climate?
Your Home says double glazed units give the best results in all climates. In hot areas a low SHGC matters most. Ask for glass that cuts solar heat as well as heat loss.
What is a good U value for a window?
Lower is better. A single glazed aluminium window sits near 6.9 in Your Home’s examples. Double glazed timber or uPVC sits near 3.0.
Do awning windows seal better than sliding windows?
Your Home says awning and casement windows seal by compression. That gives better control of air leakage than sliding windows and doors. Sliding windows open wider though, at about 45% of the window area.
Can better glass reduce condensation?
Yes, efficient glazing keeps the inside glass closer to room temperature. Your Home says this reduces condensation and the mould that can follow. Good ventilation still helps.
